New and Ancient Trace Makers

Trace fossils that are older than known animal fossils may have been formed by large unicellular organisms such as amoebas

Development of body mass and sexual size dimorphism in Danish red foxes (Vulpes vulpes)

<span class="fontstyle0">In this study, we examine the development of body mass and sexual size dimorphism (SSD) in 178 juvenile wild Danish red </span><span class="fontstyle0">foxes </span><span class="fontstyle0">from 99 litters </span><span class="fontstyle0">using </span><span class="fontstyle0">piecewise analyses of regression lines for age </span><span class="fontstyle2">versus</span><span class="fontstyle0"> weight</span><span class="fontstyle0">. When fox cubs are younger than 100 days, only slight (SSD=1.7%) and no significant difference</span><span class="fontstyle0"> (t-test: t=1.2, p=0.24) </span><span class="fontstyle0">was found in the mean weight of </span><span class="fontstyle0">males (2.03± kg) and females (1.93± kg), and</span><span class="fontstyle0"> no significant difference was found in the slope of regression lines </span><span class="fontstyle0">for </span><span class="fontstyle0">males and females </span><span class="fontstyle0">(F=0.97E-5, p = 0.99). In the growth period between 100 days of age and mating around 275 days of age, the regression line in males steepens more than that of females (difference in slopes, F=5.9, p&lt;0.02) and the difference in mean weight of the sexes become highly significant (SSD=7.4%, difference in mean t=4.6, p=2.2E-5). After mating the growth curve levels off i.e. the slope of the regression lines for age </span><span class="fontstyle2">versus</span><span class="fontstyle0"> weight is not significantly different from zero. Yearly variation was revealed in the growth rate of juvenile foxes (difference in slope for males; F=3.9, p&lt;0.01 and females; F=8.6, p&lt;0.001). Conclusion: SSD in red foxes mainly develop </span><span class="fontstyle0">as a result of a faster grow rate in males </span><span class="fontstyle0">between indepency and maturity. Ontogony of red foxes may genetically be disposed to prevent males outcompeting females in the early stages of life (&lt;100 days), when cubs are still fed by adults and the increase in SSD before mating, may be an adaption to selective forces benefitting larger males. </span><span class="fontstyle0">The growth rate of juvenile foxes of both sexes is influenced by environmental variation in different years.</span> <br /

Future permafrost conditions along environmental gradients in Zackenberg, Greenland

The future development of ground temperatures in permafrost areas is determined by a number of factors varying on different spatial and temporal scales. For sound projections of impacts of permafrost thaw, scaling procedures are of paramount importance. We present numerical simulations of present and future ground temperatures at 10 m resolution for a 4 km long transect across the lower Zackenberg valley in northeast Greenland. The results are based on stepwise downscaling of future projections derived from general circulation model using observational data, snow redistribution modeling, remote sensing data and a ground thermal model. A comparison to in situ measurements of thaw depths at two CALM sites and near-surface ground temperatures at 17 sites suggests agreement within 0.10 m for the maximum thaw depth and 1 °C for annual average ground temperature. Until 2100, modeled ground temperatures at 10 m depth warm by about 5 °C and the active layer thickness increases by about 30%, in conjunction with a warming of average near-surface summer soil temperatures by 2 °C. While ground temperatures at 10 m depth remain below 0 °C until 2100 in all model grid cells, positive annual average temperatures are modeled at 1 m depth for a few years and grid cells at the end of this century. The ensemble of all 10 m model grid cells highlights the significant spatial variability of the ground thermal regime which is not accessible in traditional coarse-scale modeling approaches

Neoproterozoic 40Ar/39Ar mica ages mark the termination of a billion years of intraplate reworking in the Capricorn Orogen, Western Australia

The tectonic history of the Proterozoic Capricorn Orogen, Western Australia, records complex intraplate reworking lasting nearly one billion years. Although the Paleo-Mesoproterozoic reworking history is well defined in the crystalline basement of the Gascoyne Province, at the western end of the orogen, the younger reactivation history remains unclear. Four reworking events affected the orogen at 1820–1770 Ma, 1680–1620 Ma, 1320–1170 Ma, and 1030–900 Ma. These events were succeeded by a breakout in predominantly dextral strike-slip reactivation of major shear zones across the Gascoyne Province. Currently, the age of this reactivation is constrained by only one date of c. 570 Ma from a single shear zone, but field relationships imply that some of the shear zones must be older than a suite of c. 755 Ma dolerite dykes. In order to constrain the age of fault and shear zone reactivation we obtained new 40 Ar/ 39 Ar dates for mica and in situ SHRIMP U-Pb dates for xenotime within shear zones. Our results when combined with previously published data, show that reactivation occurred between 920 and 830 Ma. These dates overlap with the youngest reworking event, the 1030–900 Ma Edmundian Orogeny. Furthermore, Neoproterozoic U-Pb phosphate ages are known from the bounding cratons and faulting within the adjacent Mesoproterozoic sedimentary basins suggest this event is of regional significance. In contrast to previous suggestions that this Neoproterozoic reactivation was the result of a collision from the west, we propose that it reflects north–south compression that caused dextral strike-slip fault reactivation in the north and exhumation of the southern part of the orogen

Shifted dynamics of plankton communities in a restored lake: exploring the effects of climate change on phenology through four decades

Lake surface temperatures have increased globally in recent decades. Climate change can affect lake biota directly via enhanced water temperatures, shorter ice cover duration and prolonged stratification, and indirectly via changes in species interactions. Changes in the seasonal dynamics of phytoplankton and zooplankton can further affect whole lake ecosystems. However, separating the effects of climate change from the more direct and dominating effects of nutrients is a challenge. Our aim was to explore the ecological effects of climate change while accounting for the effects of re-oligotrophication in Lake Mjøsa, the largest lake in Norway. While restoration measures since the 1970s have resulted in strongly reduced nutrient levels, the surface water temperature has increased by almost 0.4°C decade-1 during the same period. We analysed long-term trends and abrupt changes in environmental and biological time series as well as changes in the seasonal dynamics of individual plankton taxa. The general long-term trends in phenology were diverging for phytoplankton (later peaks) vs. zooplankton (earlier peaks). However, individual taxa of both phytoplankton and zooplankton displayed earlier peaks. Earlier peaks of the phytoplankton group Cryptophyceae can be explained by increased spring temperature or other climate-related changes. Earlier onset of population growth of certain zooplankton species (Limnocalanus macrurus and Holopedium gibberum) can also be explained by climatic change, either directly (earlier temperature increase) or more indirectly (earlier availability of Cryptophyceae as a food source). In the long run, climate-related changes in both phytoplankton and zooplankton phenology may have implications for the fish communities of this lake.publishedVersio

Low‐Fe(III) Greenalite Was a Primary Mineral From Neoarchean Oceans

Banded iron formations (BIFs) represent chemical precipitation from Earth’s early oceans and therefore contain insights into ancient marine biogeochemistry. However, BIFs have undergone multiple episodes of alteration, making it difficult to assess the primary mineral assemblage. Nanoscale mineral inclusions from 2.5 billion year old BIFs and ferruginous cherts provide new evidence that iron silicates were primary minerals deposited from the Neoarchean ocean, contrasting sharply with current models for BIF inception. Here we used multiscale imaging and spectroscopic techniques to characterize the best preserved examples of these inclusions. Our integrated results demonstrate that these early minerals were low‐Fe(III) greenalite. We present potential pathways in which low‐Fe(III) greenalite could have formed through changes in saturation state and/or iron oxidation and reduction. Future constraints for ancient ocean chemistry and early life’s activities should include low‐Fe(III) greenalite as a primary mineral in the Neoarchean ocean.Plain Language SummaryChemical precipitates from Earth’s early oceans hold clues to ancient seawater chemistry and biological activities, but we first need to understand what the original minerals were in ancient marine deposits. We characterized nanoscale mineral inclusions from 2.5 billion year old banded iron formations and determined that the primary minerals were iron‐rich silicate minerals dominated by reduced iron, challenging current hypotheses for banded iron formation centered on iron oxides. Our results suggest that our planet at this time had a very reducing ocean and further enable us to present several biogeochemical mineral formation hypotheses that can now be tested to better understand the activities of early life on ancient Earth.Key PointsNeoarchean nanoparticle silicate inclusions appear to be the earliest iron mineral preserved in cherts from Australia and South AfricaOur multiscale analyses indicate that the particles are greenalite that are dominantly Fe(II) with have low and variable Fe(III) contentWe present four (bio)geochemical hypotheses that could produce low‐Fe(III) greenalitePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143747/1/grl57046_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143747/2/grl57046.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143747/3/grl57046-sup-0001-2017GL076311-SI.pd

The Glenburgh Orogeny as a record of Paleoproterozoic continent-continent collision

The Gascoyne Province lies at the western end of the Capricorn Orogen, and includes a range of Paleoproterozoic gneisses and metasedimentary basins, known as the Glenburgh Terrane, that are exotic to both the Yilgarn and Pilbara Cratons. Here we present sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages for a variety of detrital zircons and metamorphic zircon and monazite from several of these pre-collisional siliciclastic basins that were deformed and metamorphosed at high metamorphic grade during the Glenburgh Orogeny, when the Yilgarn Craton collided with a previously assembled Pilbara Craton – Glenburgh Terrane. The precursors to the Moogie Metamorphics were deposited sometime between 2240 and 2125 Ma in either a foreland basin to the Ophthalmian Orogeny, or a retro-arc that formed during the collision of the Glenburgh Terrane with the Pilbara Craton. The Quartpot Pelite of the Camel Hills Metamorphics was deposited between 2000 Ma and 1985 Ma as a fore-arc deposit to the Dalgaringa continental margin arc. The Petter Calc-silicate of the Camel Hills Metamorphics was deposited sometime between 2610 and 1965 Ma as part of the Yilgarn Craton passive margin. Metamorphic zircon and monazite ages indicate that continental collision and high-grade metamorphism during the Glenburgh Orogeny (D2g) took place between 1965 Ma and 1950 Ma

The Lyngen Gabbro: the lower crust of an Ordovician Incipient-Arc

We present evidence for the origin of the Lyngen Gabbro of the Ordovician Lyngen Magmatic Complex in Troms, Northern Norway. The two magmatic suites of the Lyngen Gabbro strike parallel NNE-SSW, and have distinct magmatic signatures. We define these signatures by using major and trace-element analyses together with selected major- and trace-element mineral analyses and 143Nd/144Nd-isotope whole-rock analyses of gabbroic to tonalitic plutonic rocks from seven detailed cross-sections from this large gabbro-complex. The Western suite of the Lyngen Gabbro precipitated from magma that may have been derived from the same system as the associated volcanic rocks. The gabbros have high An-content (An>90) of their plagioclases relative to co-existing mafic minerals. Together with somewhat high ɛNd(t) values (+6), this implies that the parental magmas were hydrous tholeiites similar to those found in back arc basins today. The Eastern suite, on the other hand, consist of cumulates that were precipitated from melts resembling those of ultra-depleted high-Ca boninitic magmas found in fore-arcs. Extremely high-An plagioclases (An>95) co-exist with evolved mafic minerals and oxides, and the ɛNd(t) values are lower (+4) than in the Western suite. The Eastern suite has no volcanic counterpart, but dikes intersecting the suites have compositions that possibly represent its parental magma. The oceanic Rypdalen Shear Zone generally separates the two suites in the north, but several non-tectonic transitions from boninitic to tholeiitic signatures southwards advocate that the magmatism happened concurrently. The magmatic proximity between the suites, the hydrous magmatism and the absence of a silicic or calc-alkaline mature arc section, suggests that the Lyngen Gabbro formed in the Iapetus Ocean under conditions presently found in incipient arcs later emplaced as outer arc highs